<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style type="text/css">
		form{
			width: 300px;
			height: 300px;
			background: red url() 0 0 no-repeat;
		}
	</style>
	<script type="text/javascript">
		window.onload= function () {
			btn = document.getElementById('btn');
			word = document.getElementById('word');
			form = document.getElementById('form');

			btn.onclick = function () {
				
				oldData = form.innerHTML;

				form.innerHTML = oldData+"<br>"+word.value+"：<input type=\"text\" name=\"\">";
			}
		}
	</script>
</head>
<body>
	<form id="form">
		用户名：<input type="text" name="">
	</form>
	<input type="text" id="word" name="">
	<button id="btn">增加</button>
</body>
</html>